Copper produced by smelting is frequently electrorefined. For this reason, the molten copper product must be suitable for casting anodes. This makes it necessary to refine the copper to remove substantial quantities of dissolved sulphur and oxygen in order to cast desirable anodes. If the metal were cast directly, the high level of sulphur (typically 0.05%) and dissolved oxygen (typically 0.5%) would combine to form SO.sub.2 blisters in the cast metal. The purpose of in-line refining, as practiced with the present invention, is to remove sulphur from the molten copper. This is done in two steps: "blowing" and "poling". Blowing is the oxygenating step, wherein the sulphur is oxidized (to SO.sub.2), lowering the sulphur level (to typically 0.003%) in the molten copper. Typically, an oxygen content of 0.4% to 0.6% is required in the molten copper, as a good thermodymic condition for facilitating oxidation of the impurities. Poling--introducing hydrocarbon into the melt--reduces the oxygen content and minimizes the formation of copper oxide during solidification.
The present invention is directed to improvements in apparatus for the oxygenation of molten copper. In one process for in-line copper refining, molten copper is subjected to oxygenation during the refining process. One method of oxygenating the copper is by passing a stream of oxygen through a porous plug into the molten metal. An experimental arrangement was undertaken to determine the feasibility of this procedure in certain in-line refining procedures. In the procedure, a porous plug was used to bubble oxygen into a molten metal, which metal was to be moved past the porous plug by gravity. However, a high-temperature reaction between the oxygen and steel tubing and porous plug cover portions occurred, melting the steel. The steel industry equipment, even though developed for use with much higher molten metal temperatures, failed at molten copper temperatures because the steel components melted.